1. Field of Invention
This invention relates to a field of nuclear imaging systems and in particular to medical nuclear imaging systems involving multiple gamma cameras.
2. Description of Related Art
Nuclear imaging systems had been widely utilized to obtained anatomic and physiological information about patients at the organ and tissue level. Recent studies showed enhancement of an observation scale to provide details of various tissues and their functions at increasingly microscopic levels.
Nuclear imaging systems emission computed tomography (ECT) and transmission computed tomography (CT). ECT is generally divided into two imaging techniques: single photon computed tomography (SPECT) and positron emission tomography (PET). ECT differs from CT in that in ECT the radiation source is a radioactive agent located inside the object (e.g., a patient) being imaged and in CT, the source of radiation is located outside of the object.
In ECT studies, the distribution of radioactivity in the object is measured after administration of the radioactive agent. The radioactive agents differ for SPECT and PET application such that PET studies require the use of positron-emitting radionuclides. For all nuclear imaging protocols, the amount of the radioactive agent is limited to that acceptable for the patient. This places further restriction on amount and activity of radiation available for detection since the radiation also attenuates in the object, which in turn affects the quality of image obtained. Especially for SPECT studies, wherein attenuation is more of a problem, improvements in obtaining better quality images are needed. The time for acquiring images depends on the activity of the radioactive agent or a tracer used in the study. For humans, it is important to keep such time at a minimum because of danger of radiation to one's health and also the inconvenience of being in a confined environment. To reduce the time of imaging study, multiple cameras or detectors or a multi-head imaging systems have been used.
Using commercially available multi-head SPECT imaging systems, it is possible to keep all heads stationary and acquire dynamic planar images (2D images) or to rotate all heads at the same time wherein these heads do not rotate independently of each other and acquire tomographic SPECT images (3D images).
U.S. Pat. No. 6,150,662 to Hug et al. discloses a medical imaging system comprising multiple gamma ray detectors capable of being positioned in variety of angular positions including a position wherein one camera is substantially parallel to another camera. U.S. Pat. No. 5,760,402 to Hug et al. discloses a dual head gamma camera having two rotating heads wherein one head can be held stationary, however, these heads do not move independently of each other. These systems would allow to keep one head stationary and move or rotate the other head (but not acquire projection data at the same time) to a desired position as described by Hug et al. (U.S. Pat. Nos. 5,760,402 and 6,150,662). However, these systems were not used for acquiring projections from both heads at the same time.
U.S. Pat. No. 5,444,252 to Hug et al. discloses a system for reducing the imaging time required to generate SPECT images. FIGS. 2A-2C depict two detectors having their image direction arrows oriented at 90 degrees to reduce the imaging time of a 180 degree scan to a ½ of the imaging time of a single head system because data is acquired from two stops simultaneously.
However, rotations described by patents to Hug et al. are just for pre-positioning the camera heads before acquiring data and not for imaging while in rotation. Thus using these systems, it is possible to acquire planar dynamic images of, for example, kidneys (or VOI) or dynamic SPECT images of, for example, kidneys (or VOI) but it does not provide for acquiring images simultaneously.
Simultaneous acquisition of multiple views has been studied; however none of the studies disclose acquiring static (2D) and tomographic (3D) images at the same time.
U.S. Patent Application No. 2003/0004584 A1 to Hallett discloses a gamma camera system having a user interface capable of simultaneous acquisition of multiple views during a single study. Using a dual detector camera for SPECT studies, simultaneous acquisition of a static planar, a dynamic planar, or a gated planar views is described. Further, the disclosed interface has an option of adding the selected static, dynamic, or the gated planar view. Examples of time intervals for data acquisition include 600-700 milliseconds and 20 seconds.
U.S. 2003/0001099 A1 to Coles et al., discloses a gamma camera system having a user interface capable of simultaneous acquisition of multiple views during a single study.
Both Hallet and Coles at al., stated that the planar study where one head is stationary and the ECT study where the second head moves cannot be performed simultaneously as such studies need different head movements.
U.S. Patent Application No. 2003/0048937 A1 to Gullberg et al. discloses a method for improving the resolution of a medical imaging device using factor analysis. This method is applicable to variety of imaging devices including SPECT. Gullberg et al. disclose collecting (1) dynamic images of a canine heart using 99m TC-teboroxime with a three-detector IRIX scanner (Marconi Imaging Systems, Inc., Cleveland, Ohio) to acquire transmission and emission projection data by slow rotation every 6 seconds for 18 minutes and (2) dynamic images resulting from a planar 99m TC-MAG3 renal study using an eCam system (Siemens, Hoffman Estates, Ill.), wherein the images were acquired every 5 seconds. Gullberg et al. do not describe using a stationary detector contemporaneously with rotating detectors. This application does not disclose acquiring 2D and 3D data concomitantly during the study time.
U.S. Patent Application No. 2003/0108147 A1 to Kojima et al. discloses a radiological imaging apparatus suitable for SPECT (and PET) examination as well as other imaging applications. This reference discloses using multiple detectors disposed around a cavity (a through-hole) wherein a source of radiation (a patient) is located. Multiple detectors are arranged in the radial, axial and circumferential direction of the cavity. The reference discloses using three or more radiation detectors simultaneously to enhance accuracy. Pairing-up detectors that are mounted about 180 degrees apart from each other with respect to the axial center of the through-hole is described. Kojima et al. do not describe using rotating detectors.
U.S. Pat. No. 6,380,540 B1 to Maor, et al. discloses a SPECT system and a PET system using emission detectors and transmission detectors simultaneously. The emission detectors revolve by at least 180 degrees.
U.S. Pat. No. 5,471,061 to Moyers et al. discloses a method and apparatus for producing radioactive transmission measurements to form a 2-D or a 3-D image with a point source of radiation for SPECT and PET applications, wherein the point source rapidly moves in a selected path around an object. In the apparatus, detectors are disposed in a cylindrical array to register radiation projected from all angles from the source.
U.S. Pat. No. 4,755,680 to Logan discloses a tubular radiation imaging apparatus for SPECT and PET imaging having detectors disposed in a cylindrical array.
U.S. Pat. No. 5,629,971 to Jones et al. discloses a gamma camera and a method for SPECT studies having multiple rotatable detectors (capable of collecting emission image data and transmission image data) and multiple line sources emitting radiation, wherein each detector is associated with a particular line source. The line sources are used to gather transmission data in generating attenuation correction maps.
The disadvantage of the planar images is that the counts from different organs may be superimposed. Currently available 3D images do not provide sufficient clarity and have a significant amount of noise. Using a tracer that has a fast disappearance rate, would not allow comparing static 2D and ECT 3D data if these studies were conducted sequentially and therefore require a repetitive exposure of a patient to an additional dose of radiation.
Another approach to imaging is a dynamic SPECT imaging in which data are acquired during a slow rotation of a camera using a standard tomographic protocol. In this method, a 4D image (a series of 3D) can be collected and each time-frame of such 4D image can be viewed as 2D or 3D as well as played as a 3D movie.
Sitek et al. conducted nuclear medicine renal study by measuring the clearance of radiopharmaceuticals from kidneys utilizing 99mTc-mercaptoacetyltriglycyne (MAG3) (see Reconstruction of Dynamic Renal Tomographic Data Acquired by Slow Rotation JNM Vol. 42 No. 11, pp. 1704-1712). In the study, dynamic SPECT data acquisition was performed by slow rotation of detectors.
Similarly, Celler et al. disclose using the dynamic SPECT imaging (dSPECT) method for renal studies (see Preliminary results of a clinical validation of the dSPECT method for determination of renal glomerular filtration rate (GFR), presented at the IEEE MIC 2001, October 2001).
Thus, despite the foregoing developments, there is still a need in the art for nuclear imaging systems that can provide better resolution obtained in a reasonable amount of time and without the use of additional radiation. Further, there is a need for nuclear imaging systems which can provide quantitative imaging.
All references cited herein are incorporated herein by reference in their entireties.